Generally, an electric oil pump (EOP) includes a brushless DC motor (BLDC motor). The brushless motor keeps the characteristics of a three-phase DC motor while removing a brush serving as a commutator in a general three-phase DC motor, and further includes a rotor formed of a permanent magnet and a stator around which three coils (U-phase, V-phase, and W-phase coils) are wound.
The brushless motor supplies a three-phase current to each of the U-phase, V-phase, and W-phase coils wound around the stator and allows each of the U-phase, V-phase, and W-phase coils to generate a magnetic field depending on the supplied three-phase current to rotate the rotor, which comprises the permanent magnet.
To accurately control a rotating speed of the rotor of the brushless motor, there is a need to accurately estimate a position of the rotor. A hall sensor is generally used for this purpose. The hall sensor is used to measure a rotating position and direction of the motor by sensing a hall effect. In detail, the hall sensor may detect a relative position of the rotor to the stator based on the magnetic field generated by the permanent magnet of the rotor.
However, when the hall sensor output deviates from a predicted order, the position of the rotor may not be accurately detected. For example, a waveform is normally generated in a half period of one period of an output signal from the hall sensor which is in a failure condition. Further, a waveform corresponding to a mismatched phase is generated in the remaining half period, such that a driving voltage formed from an incorrect output signal is applied to the motor. Following this, a current conducted to the motor is increased or noise and vibration produced by the motor is increased. Accordingly, the rotation of the motor is likely to become unstable.
When the brushless motor is abnormally operated due to the failure of the hall sensor, the electric oil pump may not smoothly produce an oil pressure. Therefore, the related art performs a method for controlling a motor which leaves the motor in an inertial rotating state when it is detected that the hall sensor output deviates from a predicted order, then determines which of the three phases of the hall sensor is out of order based on the output signal of the hall sensor depending on the inertial rotation, and outputs a virtual waveform depending on the determined result.
However, when oil temperature in the electric oil pump is low or an RPM is low, the motor may not smoothly allow inertial rotation due to pump resistance, and stoppage may occur. It may then be difficult to determine which of the three phases of the hall sensor are out of order, and the control of the virtual waveform may not be performed.
The matters described as the related art have been provided only for assisting in the understanding for the background of the present disclosure and should not be considered as corresponding to the related art known to those skilled in the art.